Should be possible but would require a Python plugin because you can't figure out which identifiers have been used in the function definition (at least not with an undefined number) using only regular expressions.

You just have to analyze the Python code (probably using the already defined scopes) and then highlight the variables manually using view.add_regions.

Giving an example would be hard because I can either tell you which methods can be used or I can just write the whole thing. I'll try the first because that requires less time:

Thankfully, ST2 provides some nice parsing using the syntax definition from Python. You can adapt to this essentially using `view.find_by_selector`. For examples with add_region, see "BracketHighlighter" or "SublimeLinter" plugins. The code could be quite complex but their usage is really exemplary.